Electrochemical cells with tabs

ABSTRACT

The present invention provides electrochemical cells and batteries having one or more electrically conductive tabs and carbon sheet current collectors, where the tabs are connected to the carbon sheet current collectors; and methods of connecting the tabs to the carbon based current collectors. In one embodiment, the electrically conductive tabs are metallic tabs.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation application of the PCT PatentApplication No. PCT/US2009/0036400, filed on Mar. 6, 2009, which claimspriority to U.S. Provisional Application No. 61/034880, filed on Mar. 7,2008, the disclosure of each is hereby incorporated by reference in itsentirety for all purposes.

BACKGROUND OF THE INVENTION

In recent years, the demand for high performance batteries hasincreased, driven in part by the increasingly large number of portableconsumer electronics products and growing needs of batteries for fuelefficient vehicles. Lithium-ion batteries are found in many applicationsrequiring high energy and high power densities, as they can provide highvolumetric and gravimetric efficiency in battery packs for use inportable electronic devices and in fuel-saving vehicles.

Lithium-ion cells require tabs for making the connections between theirinternal active material and external power terminals. The tabs aretypically attached directly to the current collectors. Coupling betweenthe tabs and the electrodes can be difficult especially for cells havinggraphite sheet current collectors. One reason involves differences inthe physical properties of the tabs and the current collectors. Thisdissimilarity in material properties can lead to high contact impedance,brittle joints or other unacceptable performance-related problems. Toaddress such problems, current coupling methods have involved ultrasonicwelding and resistance spot welding to achieve a secure joint betweenthe tab and pin. Unfortunately, these methods are not suitable forattaching a metallic tab to a graphite based current collector.

Therefore, there is a need to develop other tabbing methods forattaching tabs to electrochemical cells, such as lithium-ion cellshaving carbon sheet current collectors. The present invention satisfiesthese and other needs.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to electrochemical cells and batterieshaving one or more electrically conductive tabs and carbon sheet currentcollectors, where the tabs are connected to the carbon sheet currentcollectors; and methods of connecting the tabs to the carbon basedcurrent collectors. Compared to the existing cells and methods, thepresent invention offers electrochemical cells with stable metallic tabto carbon sheet connections and low contact impedance.

In one aspect, the present invention provides an electrochemical cell.The electrochemical cell includes a positive electrode comprising apositive electrode material and a positive electrode current collector,wherein the positive electrode material is in electronically conductivecontact with the positive electrode current collector; a negativeelectrode comprising a negative electrode material and a negativeelectrode current collector, wherein the negative electrode material isin electronically conductive contact with the negative electrode currentcollector; an ion conductive medium comprising an ion conductive layerand an electrolyte solution in ionically conductive contact with thepositive electrode and the negative electrode; at least one positiveelectrode tab having a first attachment end and a second attachment end,wherein the first attachment end is connected to the positive electrodecurrent collector; optionally, at least one negative electrode tabhaving a first attachment end and a second attachment end, wherein thefirst attachment end is connected to the negative electrode currentcollector; wherein the positive electrode current collector is aconductive carbon sheet selected from the group consisting of a graphitesheet, a carbon fiber sheet, a carbon foam, a carbon nanotube film and amixture thereof, each of which has an in-plane electronic conductivityof at least 1000 S/cm, and wherein the tabs are made from anelectrically conductive material, such as a metal, a metal alloy or acomposite material. In one embodiment, the metal is selected from thegroup consisting of copper, nickel, chromium, aluminum, titanium,stainless steel, gold, tantalum, niobium, hafnium, zirconium, vanadium,indium, cobalt, tungsten, beryllium and molybdenum and alloys thereof oran alloy thereof. In certain instances, the tab has protective coatingsagainst corrosion. The coatings can be any of the above metals,anodizing and oxide coatings, conductive carbon, epoxy and glues, paintsand other protective coatings. In other instances, the coatings can benickel, silver, gold, palladium, platinum, rhodium or combinationsthereof for improving conductivity of the tabs. The alloys can be acombinations of metals described herein or formed by combining themetals described above with other suitable metals known to persons ofskill in the art.

In another aspect, the present invention provides a battery. The batteryincludes a housing, a positive connector, a negative connector, aelectrochemical cell disposed in the housing, where the positive and thenegative connector are mounted on the housing. In one embodiment, thehousing is a sealed container.

In yet another aspect, the present invention provides a method ofconnecting a tab to an electrode in an electrochemical cell. The methodincludes (a) providing an electrode comprising an electrode activematerial and a carbon current collector, wherein the electrode activematerial is in electronically conductive contact with the carbon currentcollector; (b) providing a tab having a first attachment end forattaching to the electrode; and (c) connecting the first attachment endof the tab to the carbon current collector through a process selectedfrom the group consisting of riveting, conductive adhesive lamination,hot press, ultrasonic press, mechanical press, crimping, pinching,staking and a combination thereof. In certain instances, the tabs aredeposited with sealing/protective cover layers on one side or both sidesof the tabs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a tab having openings formed by using a piercing handor mechanized tool, where each opening is surrounded by four sharp edgesprotruding above the surface of the tab.

FIG. 2 illustrates a tab attached to a positive electrode carbon currentcollector through staking, where the tab has one opening.

FIG. 3 illustrates a tab attached to a positive electrode carbon currentcollector through staking, where the tab has a plurality of openings.

FIG. 4 illustrates a tabbed positive electrode prepared through stakingaccording to an embodiment of the invention.

FIG. 5 illustrates a cyclic voltammetry profile of an electrolyte withan aluminum tab. The scanning rate is 10 mV/s.

FIG. 6 illustrates a cyclic voltammetry profile of an electrolyte with agold or gold coated tab. The scanning rate is 10 mV/s.

DETAILED DESCRIPTION OF THE INVENTION

The term “alkyl”, by itself or as part of another substituent, includes,unless otherwise stated, a straight or branched chain hydrocarbonradical, having the number of carbon atoms designated (i.e. C₁₋₈ meansone to eight carbons). Examples of alkyl groups include methyl, ethyl,n-propyl, isopropyl, n-butyl, t-butyl, isobutyl, sec-butyl, n-pentyl,n-hexyl, n-heptyl, n-octyl, and the like.

The term “alkylene” by itself or as part of another substituent includesa linear or branched saturated divalent hydrocarbon radical derived froman alkane having the number of carbon atoms indicated in the prefix. Forexample, (C₁-C₆)alkylene is meant to include methylene, ethylene,propylene, 2-methylpropylene, pentylene, and the like. Perfluoroalkylenemeans to an alkylene where all the hydrogen atoms are substituted byfluorine atoms. Fluoroalkylene means to an alkylene where hydrogen atomsare partially substituted by fluorine atoms.

The terms “halo” or “halogen,” by themselves or as part of anothersubstituent, mean, unless otherwise stated, a fluorine, chlorine,bromine, or iodine atom.

The term “haloalkyl,” are meant to include monohaloalkyl andpolyhaloalkyl. For example, the term “C₁₋₄ haloalkyl” is mean to includetrifluoromethyl, 2,2,2-trifluoroethyl, 4-chlorobutyl, 3-bromopropyl,3-chloro-4-fluorobutyl and the like.

The term “perfluoroalkyl” includes an alkyl where all the hydrogen atomsin the alkyl are substituted by fluorine atoms. Examples ofperfluoroalkyl include —CF₃, —CF₂CF₃, —CF₂—CF₂CF₃, —CF(CF₃)₂,—CF₂CF₂CF₂CF₃, —CF₂CF₂CF₂CF₂CF₃ and the like.

The term “aryl” includes a monovalent monocyclic, bicyclic or polycyclicaromatic hydrocarbon radical of 5 to 10 ring atoms, which can be asingle ring or multiple rings (up to three rings), which are fusedtogether or linked covalently. More specifically the term aryl includes,but is not limited to, phenyl, biphenyl, 1-naphthyl, and 2-naphthyl, andthe substituted forms thereof.

The term “positive electrode” refers to one of a pair of rechargeablelithium-ion cell electrodes that under normal circumstances and when thecell is fully charged will have the highest potential. This terminologyis retained to refer to the same physical electrode under all celloperating conditions even if such electrode temporarily (e.g., due tocell overdischarge) is driven to or exhibits a potential below that ofthe other (the negative) electrode.

The term “negative electrode” refers to one of a pair of rechargeablelithium-ion cell electrodes that under normal circumstances and when thecell is fully charged will have the lowest potential. This terminologyis retained to refer to the same physical electrode under all celloperating conditions even if such electrode is temporarily (e.g., due tocell overdischarge) driven to or exhibits a potential above that of theother (the positive) electrode.

In one aspect, the present invention provides an electrochemical cell.The cell is composed of a positive electrode, a negative electrode, anion conductive medium in ionically conductive contact with the positiveelectrode and the negative electrode and at least one positive electrodetab having a first attachment end and a second attachment end, where thefirst attachment end is connected to the positive electrode. Thepositive electrode includes a positive electrode material and a positiveelectrode current collector, which is in electronically conductivecontact with the positive electrode material and the first attachmentend of the positive electrode tab. The first attachment end can connectto the positive electrode current collector or the positive electrodeactive material. Optionally, the electrochemical cell includes at leastone negative electrode tab having a first attachment end and a secondattachment end, where the first attachment end is connected to thenegative electrode. The first attachment end of the negative electrodetab can connect to the negative electrode current collector or thenegative electrode active material. In one embodiment, the positiveelectrode current collector is a conductive carbon sheet selected fromthe group consisting of a graphite sheet, a carbon fiber sheet, a carbonfoam, a carbon nanotube film and a mixture thereof, each of which has anin-plane electronic conductivity of at least 1000 S/cm, preferably 2000S/cm, and most preferably 3000 S/cm. In another embodiment, the negativeelectrode current collector is conductive carbon sheet selected from thegroup consisting of a graphite sheet, a carbon fiber sheet, a carbonfoam, a carbon nanotube film and a mixture thereof. The tabs arepreferably made from an electrically conductive material, such as ametal. The tabs can have an anticorrosive layer and/or conductivecoating. The contact resistance of the interface between the positiveelectrode and the metal tabs is less than 100 mOhm-cm², preferably lessthan 25, more preferably less than 20 mOhm-cm², even more preferablyless than 10 mOhm-cm², and still more preferably less than 2.5 mOhm-cm².

In some embodiments, the current collector for the electrode is anon-metal conductive substrate. Exemplary non-metal current collectorsinclude, but are not limited to, a carbon sheet such as a graphitesheet, a carbon fiber sheet, a carbon foam, a carbon nanotube film, anda mixture of the foregoing or other conducting polymeric materials.Those of skill in the art will know of these conducting polymericmaterials.

In one embodiment, the electrochemical cell has one or more tabsattached to each electrode. In one instance, each electrode has at leastone tab. In another instance, each electrode has multiple tabs. In yetanother instance, the positive electrode has multiple metal tabsattached to the positive electrode on the carbon current collector. Forexample, each electrode can have from 2 to 20 tabs. The positive and thenegative electrode can have different numbers of tabs. The tabs can bemade of a single metal, a metal alloy or a composite material.Preferably, the tabs are metallic. Suitable metals include, but are notlimited to, iron, stainless steel, copper, nickel, chromium, zinc,aluminum, tin, gold, tantalum, niobium, hafnium, zirconium, vanadium,indium, cobalt, tungsten, beryllium and molybdenum and alloys thereof oran alloy thereof. Preferably, the metal is anticorrosive. The tabs canhave anticorrosive coatings made of any of the above metals, anodizingand oxide coatings, conductive carbon, epoxy and glues, paints and otherprotective coatings. The coatings can be nickel, silver, gold,palladium, platinum, rhodium or combinations thereof for improvingconductivity of the tabs. In one instance, the tabs are made of copper,aluminum, tin or alloys thereof. The tabs can have various shapes andsizes. In general, the tabs are smaller than the current collector towhich the tabs are attached to. In one embodiment, the tabs can have aregular or an irregular shape and form. In one instance, the tabs haveL-shape, I-shape, U-shape, V-shape, inverted T-shape, rectangular-shapeor combinations of shapes. Preferably, the tabs are metal stripsfabricated into a particular shape or form. The alloys can be acombinations of metals described herein or formed by combining themetals described above with other suitable metals known to persons ofskill in the art.

Typically, each of the tabs has a first attachment end and a secondattachment end. The first attachment end is an internal end forattaching to a current collector and the second attachment end is anexternal or an open end for connecting to an external circuit. The firstattachment end can have various shapes and dimensions. In oneembodiment, the first attachment end of the tabs has a shape selectedfrom the group consisting of a circle, an oval, a triangle, a square, adiamond, a rectangle, a trapezoidal, a U-shape, a V-shape, an L-shape, arectangular-shape and an irregular shape. In one instance, the tabs arestrips with the first attachment end having a dimension of at least 500micrometers in width and 3 mm in length. In one embodiment, theattachment end has a dimension of at least 0.25 mm². In certaininstances, the dimension is from about 1 mm² to about 500 mm². Thesecond attachment end can connect either directly to an external circuitor through a conductive member. The conductive member can be a metaltab, rod or wire. The suitable metal can be copper, aluminum, iron,stainless steel, nickel, zinc, chromium, tin, gold, tantalum, niobium,hafnium, zirconium, vanadium, indium, cobalt, tungsten, beryllium andmolybdenum and alloys thereof or an alloy thereof.

In one embodiment, the tabs are in direct contact with the currentcollector. In another embodiment, the tabs are in contact with thecurrent collector through a conductive layer. The conductive layer canbe attached to the surface of the tab, for example, by depositing alayer of carbon black on the tab. The conductive layer can include aconductive filler and a binder. In one instance, the conductive filleris selected from the group consisting of carbon black, conductingpolymers, carbon nanotubes and carbon composite materials. Suitablebinders include, but are not limited to, a polymer, a copolymer or acombination thereof. Exemplary binders include, but are not limited to,polymeric binders, particularly gelled polymer electrolytes comprisingpolyacrylonitrile, poly(methylmethacrylate), poly(vinyl chloride), andpolyvinylidene fluoride and copolymers thereof. Also, included are solidpolymer electrolytes such as polyether-salt based electrolytes includingpoly(ethylene oxide) (PEO) and its derivatives, polypropylene oxide)(PPO) and its derivatives, and poly(organophosphazenes) with ethyleneoxyor other side groups. Other suitable binders include fluorinatedionomers comprising partially or fully fluorinated polymer backbones,and having pendant groups comprising fluorinated sulfonate, imide, ormethide lithium salts. Preferred binders include polyvinylidene fluorideand copolymers thereof with hexafluoropropylene, tetrafluoroethylene,fluorovinyl ethers, such as perfluoromethyl, perfluoroethyl, orperfluoropropyl vinyl ethers; and ionomers comprising monomer units ofpolyvinylidene fluoride and monomer units comprising pendant groupscomprising fluorinated carboxylate, sulfonate, imide, or methide lithiumsalts.

The tabs can be attached to the positive electrode or the negativeelectrode using a process selected from the group consisting ofriveting, conductive adhesive lamination, hot press, ultrasonic press,mechanical press, staking, crimping, pinching, and a combinationthereof. The process offers the advantages of providing strong bindingto the current collector and yet maintaining high electricalconductivity and low impedance across the junction of tab and thecurrent collector. The process is particularly suitable for attachingmetal tabs to carbon sheet.

In one embodiment, the first attachment end includes an array ofpreformed micro indentations. The tabs can have an indentation densityfrom about 1 to about 100 per square millimeter. The indentations can beproduced by either a micro indentation hand tool or an automaticindentation device. In one instance, each indentation is about 1-100 μmin depth, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70,80, 90 or 100 micrometers and about 1-500 μm in dimension, such as 1,10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180, 200, 250,300, 400, 450, 500 micrometers. The micro indentations can be eitherevenly or randomly spaced.

The tabs having an array of micro indentations are attached to thecurrent collector via mechanical pressing or riveting to provide a closecontact between the tabs and the current collector. Alternatively, thetabs are joint to the current collector through a conductive adhesivelayer or staking.

In another embodiment, the first attachment end of the tabs includes anarray of preformed micro openings having a plurality of protrusions,such as protruding edges. In one instance, the protrusions are sharpedges. The protrusions can be either generated during the process ofmaking micro openings or prepared by a separate fabrication process. Theprotrusions extend from about 0.01 mm to about 10 mm above the surfaceof the tabs and can have various shapes. For example, the protrusionscan be triangular, rectangular or circular. The micro openings can havea dimension from micrometers to millimeters. In certain instances, theprotrusions extend between about 0.01 mm to 0.04 mm, such as about 0.01,0.02, 0.03, or 0.04 mm above the surface of the tabs. Preferably, theopenings have a dimension of about 1-1000 μm. In one embodiment, themicro openings are evenly spaced. In another embodiment, the openingsare randomly distributed. The micro openings can have various shapes. Inone embodiment, the micro openings have a shape selected from the groupconsisting of a circle, an oval, a triangle, a square, a diamond, arectangle, a trapezoidal, a rhombus, a polygon and an irregular shape.

The tabs having an array of micro openings with protrusions are weldedto the current collector through a conductive adhesive layer or bystaking, mechanical pressing, staking, riveting or a combination ofprocesses and techniques. The electrically conductive adhesives aregenerally known to persons of skill in the art. For example, certainconductive adhesives are commercially available from 3M corporation,Aptek laboratories, Inc. and Dow Corning. Exemplary electricallyconductive adhesive include, but are not limited to, urethane adhesive,silicone adhesive and epoxy adhesive.

The tabs applicable for the positive electrode as described above canalso be used for the negative electrode. In one embodiment, the negativeelectrode has a carbon current collector.

In one embodiment, the pores in the carbon current collector can besealed with resins, for example, by treating, contacting of the carboncurrent collector with resins. The resins can be conductive resins ornon-conductive resins known to a person of skill in the art. Exemplaryconductive resins are described in U.S. Pat. Nos. 7,396,492, 7,338,623,7,220,795, 6,919,394, 6,894,100, 6,855,407, 5,371,134, 5,093,037,4,830,779, 4,772,422, 6,565,772 and 6,284,817. Exemplary non-conductiveresins, for example, in adhering, sealing and coating include, but arenot limited to, epoxy resin, polyimide resin and other polymer resinsknown to persons skill in the art.

In one embodiment, FIG. 1 shows a metallic tab 110 having twodiamond-shape openings 130 and 132. Openings can have various othershapes including, but not limiting to, a circle, an oval, a triangle, asquare, a diamond, a rectangle, a trapezoidal, a U-shape, a V-shape, anL-shape, a rectangular-shape and an irregular shape. Exemplary metalsfor tab include, but are not limited to, copper, aluminum, iron,stainless steel, nickel, chromium, zinc, aluminum, tin, gold, tantalum,niobium, hafnium, zirconium, vanadium, indium, cobalt, tungsten,beryllium and molybdenum and alloys thereof or an alloy thereof. The tabcan have a protective layer such as an anticorrosive coating or aconductive layer. The materials for the anticorrosive layer can be anyof the metals above, anodizing and oxide coatings, conductive carbon,epoxy and glues, paints and other protective coatings. The conductivelayer can include metals selected from nickel, silver, gold, palladium,platinum, rhodium or alloys thereof. Opening 130 has four sharptriangular edges 121, 123, 125 and 127. Opening 132 has four sharptriangular edges 120, 122, 124 and 126. The triangular edges areprotruding above the surface of tab 110. The diamond-shape openings canbe generated by piercing using a diamond shaped tool. Those of skill inthe art will recognize that other piercing tools can also be used toproduce openings with a various shapes and numbers of protruding edges.

FIG. 2 shows another embodiment of the invention. Electrode 210 includescurrent collector layer 212 and electrode active material layer 214. Theelectrode can be either a positive or a negative electrode. Metal tab240 has an opening 220 with four sharp protruding edges 230, 232, 234and 236. Tab 240 is firmly pressed against the electrode 210 on the sideof current collector 212 resulting in the piercing of electrode 210.Alternatively, tab 240 can also be attached to the side of electrodeactive material layer 214. The protrusions have effectively riveted thepositive electrode to the current collecting tab.

FIG. 3 shows another embodiment of the invention. Tab 310 havingmultiple pierced openings as represented by 320 are riveted ontopositive electrode 330. The multiple openings have provided a strong anddurable physical contact between tab 310 and electrode 330 to ensure aminimal electronic impedance.

FIG. 4 shows a prototype of electrochemical cell having tabs attached tothe electrodes according to another embodiment of the invention.

FIG. 5 shows a cyclic voltammetry diagram of an electrolyte in thepresence of an aluminum tab according to an embodiment of the presentinvention. FIG. 5 shows an oxidation potential at 3.7 V indicating theonset of corrosion occurs at about 3.7 V. In one instance, the scan rateis 10 mv/s. In certain instances, the electrolytes are compounds havingformula (I). In other instances, the electrolytes are compounds havingthe formula: a compound having the formula: (R^(a)SO₂)N⁻Li⁺(SO₂R^(a)),wherein each R^(a) is independently C₁₋₈perfluoroalkyl or perfluoroaryl.In one instance, the electrolyte is lithiumbis(trifluoromethanesulfonyl)amide (LiTfsi). Various electrolytes asdescribed below can be used. In one instance, the electrolyte has aconcentration of 1.2 M. Various solvents as described below can be used.Exemplary solvents include a mixture of ethylene carbonate, dimethylcarbonate, and ethylmethyl carbonate at a ratio of 1:1:1 or a mixture ofethylene carbonate/diethyl carbonate at a ratio of 1:1.

FIG. 6 shows a comparison cyclic voltammetry diagram of an electrolytein the presence of a gold tab according to an embodiment of the presentinvention. In certain instances, the electrolytes are compounds havingformula (I). In other instances, the electrolytes are compounds havingthe formula: a compound having the formula: (R^(a)SO₂)N⁻Li⁺(SO₂R^(a)),wherein each R^(a) is independently C₁₋₈perfluoroalkyl or perfluoroaryl.In one instance, the electrolyte is lithiumbis(trifluoromethanesulfonyl)amide (LiTfsi). FIG. 6 shows that nooxidation occurs until about 4.5 V. In one instance, the scan rate is 10mv/s. In one instance, the electrolyte is lithiumbis(trifluoromethanesulfonyl)amide (LiTfsi). Various electrolyte asdescribed below can be used. In one instance, the electrolyte has aconcentration of 1.2 M. Various solvents as described below can be used.Exemplary solvents include a mixture of ethylene carbonate, dimethylcarbonate, and ethylmethyl carbonate at a ratio of 1:1:1 or a mixture ofethylene carbonate/diethyl carbonate at a ratio of 1:1.

In one embodiment, the present invention provides a positive electrode,which includes electrode active materials and a current collector. Thepositive electrode has an upper charging voltage of 3.5-4.5 volts versusa Li/Li⁺ reference electrode. The upper charging voltage is the maximumvoltage to which the positive electrode may be charged at a low rate ofcharge and with significant reversible storage capacity. In someembodiments, cells utilizing positive electrode with upper chargingvoltages from 3-5.8 volts versus a Li/Li⁺ reference electrode are alsosuitable. A variety of positive electrode active materials can be used.Non-limiting exemplary electrode active materials include transitionmetal oxides, phosphates and sulfates, and lithiated transition metaloxides, phosphates and sulfates.

In some embodiments, the electrode active materials are oxides withempirical formula Li_(x)MO₂, where M is a transition metal ions selectedfrom the group consisting of Mn, Fe, Co, Ni, Al, Mg, Ti, V, and acombination thereof, with a layered crystal structure, the value x maybe between about 0.01 and about 1, suitably between about 0.5 and about1, more suitably between about 0.9 to 1. In yet some other embodiments,the active materials are oxides with empirical formulaLi_(1+x)M_(2-y)O₄, where M is a transition metal ions selected from thegroup consisting of Mn, Co, Ni, Al, Mg, Ti, V, and a combinationthereof, with a spinel crystal structure, the value x may be betweenabout −0.11 and 0.33, suitably between about 0 and about 0.1, the valueof y may be between about 0 and 0.33, suitably between 0 and 0.1. In yetsome other embodiments the active materials are vanadium oxides such asLiV₂O₅, LiV₆O₁₃, Li_(x)V₂O₅, Li_(x)V₆O₁₃, wherein x is 0<x<1 or theforegoing compounds modified in that the compositions thereof arenonstoichiometric, disordered, amorphous, overlithiated, orunderlithiated forms such as are known in the art. The suitable positiveelectrode-active compounds may be further modified by doping with lessthan 5% of divalent or trivalent metallic cations such as Fe²⁺, Ti²⁺,Zn²⁺, Ni²⁺, Co²⁺, Cu²⁺, Mg²⁺, Cr³⁺, Fe³⁺, Al³⁺, Ni³⁺, Co³⁺, or Mn³⁺, andthe like. In some other embodiments, positive electrode active materialssuitable for the positive electrode composition include lithiuminsertion compounds with olivine structure such as Li_(x)MXO₄ where M isa transition metal ions selected from the group consisting of Fe, Mn,Co, Ni, and a combination thereof, and X is a selected from a groupconsisting of P, V, S, Si and combinations thereof, the value of thevalue x may be between about 0 and 2. In some other embodiments, theactive materials with NASICON structures such as Y_(x)M₂(XO₄)₃, where Yis Li or Na, or a combination thereof, M is a transition metal ionselected from the group consisting of Fe, V, Nb, Ti, Co, Ni, Al, or thecombinations thereof, and X is selected from a group of P, S, Si, andcombinations thereof and value of x between 0 and 3. The examples ofthese materials are disclosed by J. B. Goodenough in “Lithium IonBatteries” (Wiley-VCH press, Edited by M. Wasihara and O. Yamamoto).Particle size of the electrode materials are preferably between 1 nm and100 μm, more preferably between 10 nm and 100 μm, and even morepreferably between 1 μm and 100 μm.

In some embodiments, the electrode active materials are oxides such asLiCoO₂, spinel LiMn₂O₄, chromium-doped spinel lithium manganese oxidesLi_(x)Cr_(y)Mn₂O₄, layered LiMnO₂, LiNiO₂, LiNi_(x)Co_(1−x)O₂ where x is0<x<1, with a preferred range of 0.5<x<0.95, and vanadium oxides such asLiV₂O₅, LiV₆O₁₃, Li_(x)V₂O₅, Li_(x)V₆O₁₃, where x is 0<x<1, or theforegoing compounds modified in that the compositions thereof arenonstoichiometric, disordered, amorphous, overlithiated, orunderlithiated forms such as are known in the art. The suitable positiveelectrode-active compounds may be further modified by doping with lessthan 5% of divalent or trivalent metallic cations such as Fe²⁺, Ti²⁺,Zn²⁺, Ni²⁺, Co²⁺, Cu²⁺, Mg²⁺, Cr³⁺, Fe³⁺, Al³⁺, Ni³⁺, Co³⁺, or Mn³⁺, andthe like. In some other embodiments, positive electrode active materialssuitable for the positive electrode composition include lithiuminsertion compounds with olivine structure such as LiFePO₄ and withNASICON structures such as LiFeTi(SO₄)₃, or those disclosed by J. B.Goodenough in “Lithium Ion Batteries” (Wiley-VCH press, Edited by M.Wasihara and O. Yamamoto). In yet some other embodiments, electrodeactive materials include LiFePO₄, LiMnPO₄, LiVPO₄, LiFeTi(SO₄)₃,LiNi_(x)Mn_(1−x)O₂, LiNi_(x)Co_(y)Mn_(1−x-y)O₂ and derivatives thereof,wherein x is 0<x<1 and y is 0<y<1. In certain instances, x is betweenabout 0.25 and 0.9. In one instance, x is ⅓ and y is ⅓. Particle size ofthe positive electrode active material should range from about 1 to 100microns. In some preferred embodiments, transition metal oxides such asLiCoO₂, LiMn₂O₄, LiNiO₂, LiNi_(x)Mn_(1−x)O₂, LiNi_(x)Co_(y)Mn_(1−x-y)O₂and their derivatives, where x is 0<x<1 and y is 0<y<1.LiNi_(x)Mn_(1−x)O₂ can be prepared by heating a stoichiometric mixtureof electrolytic MnO₂, LiOH and nickel oxide to about 300 to 400° C. Insome other embodiments, the electrode active materials arexLi₂MnO₃(1−x)LiMO₂ or LiM′PO₄, where M is selected from Ni, Co, Mn,LiNiO₂ or LiNi_(x)Co_(1−x)O₂; M′ is selected from the group consistingof Fe, Ni, Mn and V; and x and y are each independently a real numberbetween 0 and 1. LiNi_(x)Co_(y)Mn_(1−x-y)O₂ can be prepared by heating astoichiometric mixture of electrolytic MnO₂, LiOH, nickel oxide andcobalt oxide to about 300 to 500° C. The positive electrode may containconductive additives from 0% to about 90%, preferably the additive isless than 5%. In one embodiment, the subscripts x and y are eachindependently selected from 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45,0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 or 0.95. x and y can beany numbers between 0 and 1 to satisfy the charge balance of thecompounds LiNi_(x)Mn_(1−x)O₂and LiNi_(x)Co_(y)Mn_(1−x-y)O₂.

Representative positive electrodes and their approximate rechargedpotentials include FeS₂ (3.0 V vs. Li/Li⁺), LiCoPO₄ (4.8 V vs. Li/Li⁺),LiFePO₄ (3.45 V vs. Li/Li⁺), Li₂FeS₂ (3.0 V vs. Li/Li⁺), Li₂FeSiO₄ (2.9V vs. Li/Li⁺), LiMn₂O₄ (4.1 V vs. Li/Li⁺), LiMnPO₄ (4.1 V vs. Li/Li⁺),LiNiPO₄ (5.1 V vs. Li/Li⁺), LiV₃O₈ (3.7 V vs. Li/Li⁺), LiV₆O₁₃ (3.0 Vvs. Li/Li⁺), LiVOPO₄ (4.15 V vs. Li/Li⁺), LiVOPO₄F (4.3 V vs. Li/Li⁺),Li₃ V₂(PO₄)₃ (4.1 V (2 Li) or 4.6 V (3 Li) vs. Li/Li⁺), MnO₂ (3.4 V vs.Li/Li⁺), MoS₃ (2.5 V vs. Li/Li⁺), sulfur (2.4 V vs. Li/Li⁺), TiS₂(2.5 Vvs. Li/Li⁺), TiS₃ (2.5 V vs. Li/Li⁺), V₂O₅ (3.6 V vs. Li/Li⁺), V₆O₁₃(3.0 V vs. Li/Li⁺), and combinations thereof.

A positive electrode can be formed by mixing and forming a compositioncomprising, by weight, 0.01-15%, preferably 2-15%, more preferably 4-8%,of a polymer binder, 10-50%, preferably 15-25%, of the electrolytesolution of the invention herein described, 40-85%, preferably 65-75%,of an electrode-active material, and 1-12%, preferably 4-8%, of aconductive additive. Optionally, up to 12% of inert filler may also beadded, as may such other adjuvants as may be desired by one of skill inthe art, which do not substantively affect the achievement of thedesirable results of the present invention. In one embodiment, no inertfiller is used.

In one embodiment, the present invention provides a negative electrode,which includes electrode active materials and a current collector. Thenegative electrode comprises either a metal selected from the groupconsisting of Li, Si, Sn, Sb, Al and a combination thereof, or a mixtureof one or more negative electrode active materials in particulate form,a binder, preferably a polymeric binder, optionally an electronconductive additive, and at least one organic carbonate. Examples ofuseful negative electrode active materials include, but are not limitedto, lithium metal, carbon (graphites, coke-type, mesocarbons,polyacenes, carbon nanotubes, carbon fibers, and the like). Negativeelectrode-active materials also include lithium-intercalated carbon,lithium metal nitrides such as Li_(2.6)Co_(0.4)N, metallic lithiumalloys such as LiAl or Li₄Sn, lithium-alloy-forming compounds of tin,silicon, antimony, or aluminum such as those disclosed in“Active/Inactive Nanocomposites as Anodes for Li-Ion Batteries,” by Maoet al. in Electrochemical and Solid State Letters, 2 (1), p. 3, 1999.Further included as negative electrode-active materials are metal oxidessuch as titanium oxides, iron oxides, or tin oxides. When present inparticulate form, the particle size of the negative electrode activematerial should range from about 0.01 to 100 microns, preferably from 1to 100 microns. Some preferred negative electrode active materialsinclude graphites such as carbon microbeads, natural graphites, carbonnanotubes, carbon fibers, or graphitic flake-type materials. Some otherpreferred negative electrode active materials are graphite microbeadsand hard carbon, which are commercially available.

A negative electrode can be formed by mixing and forming a compositioncomprising, by weight, 0.01-20%, or 1-20%, preferably 2-20%, morepreferably 3-10%, of a polymer binder, 10-50%, preferably 14-28%, of theelectrolyte solution of the invention herein described, 40-80%,preferably 60-70%, of electrode-active material, and 0-5%, preferably1-4%, of a conductive additive. Optionally up to 12% of an inert filleras hereinabove described may also be added, as may such other adjuvantsas may be desired by one of skill in the art, which do not substantivelyaffect the achievement of the desirable results of the presentinvention. It is preferred that no inert filler be used.

Suitable conductive additives for the positive and negative electrodecomposition include carbons such as coke, carbon black, carbonnanotubes, carbon fibers, and natural graphite, metallic flake orparticles of copper, stainless steel, nickel or other relatively inertmetals, conductive metal oxides such as titanium oxides or rutheniumoxides, or electronically-conductive polymers such as polyacetylene,polyphenylene and polyphenylenevinylene, polyaniline or polypyrrole.Preferred additives include carbon fibers, carbon nanotubes and carbonblacks with relatively surface area below ca. 100 m²/g such as Super Pand Super S carbon blacks available from MMM Carbon in Belgium.

The current collector suitable for the positive and negative electrodesincludes a metal foil and a carbon sheet selected from a graphite sheet,carbon fiber sheet, carbon foam and carbon nanotubes sheet or film. Highconductivity is generally achieved in pure graphite and carbon nanotubesfilm so it is preferred that the graphite and nanotube sheeting containas few binders, additives and impurities as possible in order to realizethe benefits of the present invention. Carbon nanotubes can be presentfrom 0.01% to about 99%. Carbon fiber can be in microns or submicrons.Carbon black or carbon nanotubes may be added to enhance theconductivities of the certain carbon fibers. In one embodiment, thenegative electrode current collector is a metal foil, such as copperfoil. The metal foil can have a thickness from about 5 to about 300micrometers.

The carbon sheet current collector suitable for the present inventionmay be in the form of a powder coating on a substrate such as a metalsubstrate, a free-standing sheet, or a laminate. That is the currentcollector may be a composite structure having other members such asmetal foils, adhesive layers and such other materials as may beconsidered desirable for a given application. However, in any event,according to the present invention, it is the carbon sheet layer, orcarbon sheet layer in combination with an adhesion promoter, which isdirectly interfaced with the electrolyte of the present invention and isin electronically conductive contact with the electrode surface.

In some embodiments, resins are added to fill into the pores of carbonsheet current collectors to prevent the passing through of electrolyte.The resin can be conductive or non-conductive. Non-conductive resins canbe used to increase the mechanical strength of the carbon sheet. The useof conductive resins have the advantage of increasing initial chargeefficiency, decrease surface area where passivation occurs due to thereaction with the electrolyte. The conductive resin can also increasethe conductivity of the carbon sheet current collector.

The flexible carbon sheeting preferred for the practice of the presentinvention is characterized by a thickness of at most 2000 micrometers,with less than 1000, preferred, less than 300 more preferred, less than75 micrometers even more preferred, and less than 25 micrometers mostpreferred. The flexible carbon sheeting preferred for the practice ofthe invention is further characterized by an electrical conductivityalong the length and width of the sheeting of at least 1000 Siemens/cm(S/cm), preferably at least 2000 S/cm, most preferably at least 3000S/cm measured according to ASTM standard C611-98.

The flexible carbon sheeting preferred for the practice of the presentinvention may be compounded with other ingredients as may be requiredfor a particular application, but carbon sheet having a purity of ca.95% or greater is highly preferred. In some embodiments, the carbonsheet has a purity of greater than 99%. At a thickness below about 10μm, it may be expected that electrical resistance could be unduly high,so that thickness of less than about 10 μm is less preferred.

In some embodiments, the carbon current collector is a flexiblefree-standing graphite sheet. The flexible free-standing graphite sheetcathode current collector is made from expanded graphite particleswithout the use of any binding material. The flexible graphite sheet canbe made from natural graphite, Kish flake graphite, or syntheticgraphite that has been voluminously expanded so as to have d₀₀₂dimension at least 80 times and preferably 200 times the original d₀₀₂dimension. Expanded graphite particles have excellent mechanicalinterlocking or cohesion properties that can be compressed to form anintegrated flexible sheet without any binder. Natural graphites aregenerally found or obtained in the form of small soft flakes or powder.Kish graphite is the excess carbon which crystallizes out in the courseof smelting iron. In one embodiment, the current collector is a flexiblefree-standing expanded graphite. In another embodiment, the currentcollector is a flexible free-standing expanded natural graphite.

A binder is optional, however, it is preferred in the art to employ abinder, particularly a polymeric binder, and it is preferred in thepractice of the present invention as well. One of skill in the art willappreciate that many of the polymeric materials recited below assuitable for use as binders will also be useful for formingion-permeable separator membranes suitable for use in the lithium orlithium-ion battery of the invention.

Suitable binders include, but are not limited to, polymeric binders,particularly gelled polymer electrolytes comprising polyacrylonitrile,poly(methylmethacrylate), poly(vinyl chloride), and polyvinylidenefluoride and copolymers thereof. Also, included are solid polymerelectrolytes such as polyether-salt based electrolytes includingpoly(ethylene oxide) (PEO) and its derivatives, poly(propylene oxide)(PPO) and its derivatives, and poly(organophosphazenes) with ethyleneoxyor other side groups. Other suitable binders include fluorinatedionomers comprising partially or fully fluorinated polymer backbones,and having pendant groups comprising fluorinated sulfonate, imide, ormethide lithium salts. Preferred binders include polyvinylidene fluorideand copolymers thereof with hexafluoropropylene, tetrafluoroethylene,fluorovinyl ethers, such as perfluoromethyl, perfluoroethyl, orperfluoropropyl vinyl ethers; and ionomers comprising monomer units ofpolyvinylidene fluoride and monomer units comprising pendant groupscomprising fluorinated carboxylate, sulfonate, imide, or methide lithiumsalts.

Gelled polymer electrolytes are formed by combining the polymeric binderwith a compatible suitable aprotic polar solvent and, where applicable,the electrolyte salt. PEO and PPO-based polymeric binders can be usedwithout solvents. Without solvents, they become solid polymerelectrolytes, which may offer advantages in safety and cycle life undersome circumstances. Other suitable binders include so-called“salt-in-polymer” compositions comprising polymers having greater than50% by weight of one or more salts. See, for example, M. Forsyth et al,Solid State Ionics, 113, pp 161-163 (1998).

Also included as binders are glassy solid polymer electrolytes, whichare similar to the “salt-in-polymer” compositions except that thepolymer is present in use at a temperature below its glass transitiontemperature and the salt concentrations are ca. 30% by weight. In oneembodiment, the volume fraction of the preferred binder in the finishedelectrode is between 4 and 40%.

The ion conductive medium typically comprises a electrolyte solution,which includes a lithium salt of formula (I):

R¹—X⁻(Li⁺)R²(R³)_(m),   (I)

dissolved in a solvent. The ion conductive medium is preferablyelectronically insulative. The substituents R¹, R² and R³ are eachindependently an electron-withdrawing group selected from the groupconsisting of —CN, —SO₂R^(a), —SO₂-L^(a)—SO₂N⁻Li⁺SO₂R^(a),—P(O)(OR^(a))₂, —P(O)(R^(a))₂, —CO₂R^(a), —C(O)R^(a) and —H. Each R^(a)is independently selected from the group consisting of C₁₋₈ alkyl,C₁₋₈haloalkyl, C₁₋₈ perfluoroalkyl, aryl, perfluoroaryl, optionallysubstituted barbituric acid and optionally substituted thiobarbituricacid, wherein at least one carbon-carbon bond of the alkyl orperfluoroalkyl are optionally substituted with a member selected from—O— or —S— to form an ether or a thioether linkage and the aryl isoptionally substituted with from 1-5 members selected from the groupconsisting of halogen, C₁₋₄haloalkyl, C₁₋₄perfluoroalkyl, —CN,—SO₂R^(b), —P(O)(OR^(b))₂, —P(O)(R^(b))₂, —CO₂R^(b) and —C(O)R^(b),wherein R^(b) is C₁₋₈ alkyl or C₁₋₈ perfluoroalkyl, and L^(a) isC₁₋₄perfluoroalkylene. In one embodiment, R¹ is —SO₂R^(a). In someinstances, R¹ is —SO₂(C₁₋₈perfluoroalkyl). For example, R¹ is —SO₂CF₃,—SO₂CF₂CF₃ and the like. In some other instances, when m is 0, R¹ is—SO₂(C₁₋₈perfluoroalkyl) and R² is —SO₂(C₁₋₈perfluoroalkyl) or—SO₂(—R^(a)—SO₂Li⁺)SO₂—R^(a), wherein R^(a) is C₁₋₈perfluoroalkyl,optionally substituted with from 1-4 —O—. For example, each R^(a) isindependently selected from the group consisting of —CF₃, —CF₂CF₃,—CF₂—SCF₃, —CF₂—OCF₃, C₁₋₈fluoroalkyl, perfluorophenyl, trifluorophenyland bis-trifluorophenyl.

In one embodiment of compounds having formula I, R¹ is—SO₂(C₁₋₈fluoroalkyl). C₁₋₈fluoroalkyl includes alkyls having up to 17fluorine atoms and is also meant to include various partiallyfluorinated alkyls, such as —CH₂CF₃, —CH₂—OCF₃, —CF₂CH₃, —CHFCHF₂,—CHFCF₃, —CF₂CH₂CF₃ and the like.

In compounds of formula I, L^(a) is C₁₋₄perfluoroalkylene, such as—CF₂—, —CF₂CF₂—, —CF₂CF₂CF₂—, —CF₂CF₂CF₂CF₂— and isomers thereof.

The symbol X is N when m is 0. X is C when m is 1.

In certain embodiments, the compounds have the formula:(R^(a)SO₂)N⁻Li⁺(SO₂R^(a)), wherein each R^(a) is independentlyC₁₋₈perfluoroalkyl or perfluoroaryl, such as perfluorophenyl.

In certain embodiments, the compounds of formula I is selected from thegroup consisting of: CF₃SO₂N⁻(Li⁺)SO₂CF₃, CF₃CF₂SO₂N⁻(Li⁺)SO₂CF₃,CF₃CF₂SO₂N⁻(Li⁺)SO₂CF₂CF₃, CF₃SO₂N⁻(Li⁺)SO₂CF₂OCF₃,CF₃OCF₂SO₂N⁻(Li⁺)SO₂CF₂OCF₃, C₆F₅SO₂N⁻(Li⁺)SO₂CF₃,C₆F₅SO₂N⁻(Li⁺)SO₂C₆F₅and CF₃SO₂N⁻(Li⁺)SO₂PhCF₃.

In one embodiment, the compounds of formula I has a subformula Ia:

(C₁₋₈fluoroalkyl)SO₂—X⁻(Li⁺)R²(R³)_(m),   Ia

where the substituents are as defined above.

In another embodiment, the compounds of formula I has a subformula Ia-1:

(C₁₋₈fluoroalkyl)SO₂—C⁻(Li⁺)R²R³   Ia-1

where the substituents are as defined above.

In another embodiment, the compounds of formula I has a subformula Ia-2:

(C₁₋₈fluoroalkyl)SO₂—N⁻(Li⁺)R²   Ia-2

where the substituents are as defined above.

Electrolyte solvents can be aprotic liquids or polymers. Included areorganic carbonates and lactones. Organic carbonates include a compoundhaving the formula: R⁴OC(═O)OR⁵, wherein R⁴ and R⁵ are eachindependently selected from the group consisting of C₁₋₄alkyl andC₃₋₆cycloalkyl, or together with the atoms to which they are attached toform a 4- to 8-membered ring, wherein the ring carbons are optionallysubstituted with 1-2 members selected from the group consisting ofhalogen, C₁₋₄alkyl and C₁₋₄haloalkyl. In one embodiment, the organiccarbonates include propylene carbonate, dimethyl carbonate, ethylenecarbonate, diethyl carbonate, ethylmethyl carbonate and a mixturethereof as well as many related species. The lactone is selected fromthe group consisting of β-propiolactone, γ-butyrolactone,δ-valerolactone, ε-caprolactone, hexano-6-lactone and a mixture thereof,each of which is optionally substituted with from 1-4 members selectedfrom the group consisting of halogen, C₁₋₄alkyl and C₁₋₄haloalkyl. Alsoincluded are solid polymer electrolytes such as polyethers andpoly(organo phosphazenes). Further included are lithium salt-containingionic liquid mixtures such as are known in the art, including ionicliquids such as organic derivatives of the imidazolium cation withcounterions based on imides, methides, PF₆ ⁻, or BF₄ ⁻. See for example,MacFarlane et al., Nature, 402, 792 (1999). Mixtures of suitableelectrolyte solvents, including mixtures of liquid and polymericelectrolyte solvents are also suitable.

The electrolyte solution suitable for the practice of the invention isformed by combining the lithium imide or methide salts of compounds offormula I with optionally a co-salt selected from LiPF₆, LiBF₄, LiAsF₆,LiB(C₂O₄)₂, (Lithium bis(oxalato)borate), or LiClO₄, along with anon-aqueous electrolyte solvent by dissolving, slurrying or melt mixingas appropriate to the particular materials. The present invention isoperable when the concentration of the imide or methide salt is in therange of 0.2 to up to 3 molar, but 0.5 to 2 molar is preferred, with 0.8to 1.2 molar most preferred. Depending on the fabrication method of thecell, the electrolyte solution may be added to the cell after winding orlamination to form the cell structure, or it may be introduced into theelectrode or separator compositions before the final cell assembly.

The electrochemical cell optionally contains an ion conductive layer.The ion conductive layer suitable for the lithium or lithium-ion batteryof the present invention is any ion-permeable shaped article, preferablyin the form of a thin film, membrane or sheet. Such ion conductive layermay be an ion conductive membrane or a microporous film such as amicroporous polypropylene, polyethylene, polytetrafluoroethylene andlayered structures thereof. Suitable ion conductive layer also includeswellable polymers such as polyvinylidene fluoride and copolymersthereof. Other suitable ion conductive layer include those known in theart of gelled polymer electrolytes such as poly(methyl methacrylate) andpoly(vinyl chloride). Also suitable are polyethers such as poly(ethyleneoxide) and polypropylene oxide). Preferable are microporous polyolefinseparators, separators comprising copolymers of vinylidene fluoride withhexafluoropropylene, perfluoromethyl vinyl ether, perfluoroethyl vinylether, or perfluoropropyl vinyl ether, including combinations thereof,or fluorinated ionomers, such as those described in Doyle et al., U.S.Pat. No. 6,025,092.

In another aspect, the present invention provides a method of connectinga tab to an electrode in an electrochemical cell. The method includes(a) providing an electrode comprising an electrode active material and acarbon current collector in electronically conductive contact with theelectrode; (b) providing a tab having a first attachment end forattaching to the electrode; and (c) connecting the first attachment endof the tab to the carbon current collector through a process selectedfrom the group consisting of riveting, conductive adhesive lamination,staking, hot press, ultrasonic press, mechanical press, crimping,pinching, and a combination thereof. In one embodiment, theelectrochemical cell is a lithium-ion electrochemical cell.

In one embodiment, the method includes aligning the carbon currentcollector with the tab and applying riveting, staking, conductiveadhesive lamination, hot press, ultrasonic press, mechanical press,crimping, pinching, and a combination thereof to the carbon currentcollector. The tab can have various shapes, such as a U-shape, aV-shape, a L-shape, a rectangular-shape or a inverted T-shape. In oneinstance, the carbon current collector and the tab can be aligned to anydesirable position for attachment. The carbon current collector can bealigned to any suitable part of the tab. For example, the carbon currentcollector is aligned to the middle, the side or a predetermined positionof the tab. The tab and the current collector are joined togetherthrough riveting or staking.

In another embodiment, the tab is connected to the carbon currentcollector through a conductive adhesive layer. In certain instances, theconductive layer is deposited on the tab. In one instance, theconductive layer is an adhesive layer comprising a conductive filler anda binder. The conductive filler is selected from the group consisting ofcarbon black, conducting polymers, carbon nanotubes and carbon compositematerials. The conductive layer can have a thickness from about 1 nm toabout 1000 micrometers. For example, the conductive layer has athickness of about 1, 10, 20, 30, 40, 50, 60, 70, 80, 90 100, 200, 300,400, 500, 600, 700, 800, 900 or 1000 nm. The conductive layer can alsohave a thickness of about 1, 10, 20, 30, 40, 50, 60, 70, 80, 90 100,200, 300, 400, 500, 600, 700, 800, 900 or 1000 μm.

In another aspect, the present invention provides a battery. The batteryincludes a housing, a positive connector, a negative connector, aelectrochemical cell disposed in the housing, where the positive and thenegative connector are mounted on the housing. In one embodiment, thehousing is a sealed container. In yet another embodiment, the tab isconnected to the carbon current collector through a conductive adhesivelayer then riveted, hot pressed, ultrasonic pressed, mechanical pressed,staked, crimped, or pinched.

In one embodiment, both the positive connector and the negativeconnectors have an inner end disposed within the housing and an outerend protrudes outside the housing. The positive electrode tab is weldedto the inner end of the positive connector and the negative electrodetab is welded to the inner end of the negative connector to provide abattery having a positive outer end and a negative outer end forconnecting to external devices. For example, the battery can havemultiple tabs welded to the positive connector or the negativeconnector. The battery can be prepared by first attaching the tabs tothe electrodes of the lithium-ion electrochemical cell. The electrodesand separator layers are then jelly-wound or stacked and placed in abattery container. The tabs for the positive electrode are welded to theinner end of the positive connector of the housing, and the tabs for thenegative electrode are welded to the inner end of the negative connectorof the housing. The housing is sealed and no tabs are exposed. In oneembodiment, the housing is a container.

In another embodiment, the second attachment ends of the tabs of thebattery are protruded outside the housing for connecting to an externaldevice. For example, the battery can be prepared by first attaching thetabs to the electrodes of a lithium-ion electrochemical cell. Theelectrodes and separator are then jelly-wound or stacked and placed in ahousing then sealed with only the tabs are protruded outside thehousing. In one embodiment, the housing is a container.

In another embodiment, the carbon current collector for the positiveelectrode and/or the carbon current collector for the negative electrodeprotrude outside the housing. In one instance, the housing is afoil-polymer laminate package. The pores in the carbon current collectorare closed or sealed by a resin or other material to provide as close toa hermetic seal as possible when the carbon current collector(s) areheat-sealed between two layers of the foil-laminate. The resins can beconductive or non-conductive resins.

The benefit of this design is that the metal tabs can be attached to thecarbon current collectors outside of the cell and are not in contactwith the corrosive electrolyte solution. This allows the use of aplurality of metals, metal alloys or composites.

The Li-ion electrochemical cell can be assembled according to any methodknown in the art (see, U.S. Pat. Nos. 5,246,796; 5,837,015; 5,688,293;5,456,000; 5,540,741; and 6,287,722 as incorporated herein byreference). In a first method, electrodes are solvent-cast onto currentcollectors, the collector/electrode tapes are spirally wound along withmicroporous polyolefin separator films to make a cylindrical roll, thewinding placed into a metallic cell case, and the nonaqueous electrolytesolution impregnated into the wound cell. In a second method electrodesare solvent-cast onto current collectors and dried, the electrolyte anda polymeric gelling agent are coated onto the separators and/or theelectrodes, the separators are laminated to, or brought in contact with,the collector/electrode tapes to make a cell subassembly, the cellsubassemblies are then cut and stacked, or folded, or wound, then placedinto a foil-laminate package, and finally heat treated to gel theelectrolyte. In a third method, electrodes and separators are solventcast with also the addition of a plasticizer; the electrodes, meshcurrent collectors, electrodes and separators are laminated together tomake a cell subassembly, the plasticizer is extracted using a volatilesolvent, the subassembly is dried, then by contacting the subassemblywith electrolyte the void space left by extraction of the plasticizer isfilled with electrolyte to yield an activated cell, the subassembly(s)are optionally stacked, folded, or wound, and finally the cell ispackaged in a foil laminate package. In a fourth method, the electrodeand separator materials are dried first, then combined with the salt andelectrolyte solvent to make active compositions; by melt processing theelectrodes and separator compositions are formed into films, the filmsare laminated to produce a cell subassembly, the subassembly(s) arestacked, folded, or wound and then packaged in a foil-laminatecontainer. In a fifth method, electrodes and separator are eitherspirally wound or stacked; polymeric binding agent (e.g., polyvinylidene(PVDF) or equivalent) is on separator or electrodes, after winding orstacking, heat lamination to melt the binding agent and adhere thelayers together followed by electrolyte fill.

In one embodiment, the electrodes can conveniently be made bydissolution of all polymeric components into a common solvent and mixingtogether with the carbon black particles and electrode active particles.For example, a lithium battery electrode can be fabricated by dissolvingpolyvinylidene (PVDF) in 1-methyl-2-pyrrolidinone orpoly(PVDF-co-hexafluoropropylene (HFP)) copolymer in acetone solvent,followed by addition of particles of electrode active material andcarbon black or carbon nanotubes, followed by deposition of a film on asubstrate and drying. The resultant electrode will comprise electrodeactive material, conductive carbon black or carbon nanotubes, andpolymer. This electrode can then be cast from solution onto a suitablesupport such as a glass plate or a current collector, and formed into afilm using techniques well known in the art.

The positive electrode is brought into electronically conductive contactwith the graphite current collector with as little contact resistance aspossible. This may be advantageously accomplished by depositing upon thegraphite sheet a thin layer of an adhesion promoter such as a mixture ofan acrylic acid-ethylene copolymer and carbon black. Suitable contactmay be achieved by the application of heat and/or pressure to provideintimate contact between the current collector and the electrode.

The flexible carbon sheeting, such as carbon nanotubes or graphite sheetfor the practice of the present invention provides particular advantagesin achieving low contact resistance. By virtue of its high ductility,conformability, and toughness it can be made to form particularlyintimate and therefore low resistance contacts with electrode structuresthat may intentionally or unintentionally proffer an uneven contactsurface. In any event, in the practice of the present invention, thecontact resistance between the positive electrode and the graphitecurrent collector of the present invention preferably does not exceed 50ohm-cm², in one instance, does not exceed 10 ohms-cm², and in anotherinstance, does not exceed 2 ohms-cm². Contact resistance can bedetermined by any convenient method as known to one of ordinary skill inthe art. Simple measurement with an ohm-meter is possible.

The negative electrode is brought into electronically conductive contactwith an negative electrode current collector. The negative electrodecurrent collector can be a metal foil, a mesh or a carbon sheet. In oneembodiment, the current collector is a copper foil or mesh. In apreferred embodiment, the negative electrode current collector is acarbon sheet selected from a graphite sheet, carbon fiber sheet or acarbon nanotube sheet. As in the case of the positive electrode, anadhesion promoter can optionally be used to attach the negativeelectrode to the current collector.

In one embodiment, the electrode films thus produced are then combinedby lamination. In order to ensure that the components so laminated orotherwise combined are in excellent ionically conductive contact withone another, the components are combined with an electrolyte solutioncomprising an aprotic solvent, preferably an organic carbonate ashereinabove described, and a lithium imide or methide salt representedby the formula I.

While the invention has been described by way of example and in terms ofthe specific embodiments, it is to be understood that examples andembodiments described herein are for illustrative purposes only and theinvention is not limited to the disclosed embodiments. It is intended tocover various modifications and similar arrangements as would beapparent to those skilled in the art. Therefore, the scope of theappended claims should be accorded the broadest interpretation so as toencompass all such modifications and similar arrangements. Allpublications, patents, and patent applications cited herein are herebyincorporated by reference in their entirety for all purposes.

1. An electrochemical cell, said electrochemical cell comprising: apositive electrode comprising a positive electrode material and apositive electrode current collector, wherein the positive electrodematerial is in electronically conductive contact with the positiveelectrode current collector; a negative electrode comprising a negativeelectrode material and a negative electrode current collector, whereinthe negative electrode material is in electronically conductive contactwith the negative electrode current collector; an electronicallyinsulative and ion conductive medium in ionically conductive contactwith said positive electrode and said negative electrode, wherein saidionic conductive medium comprises an ion conductive layer and anelectrolyte solution; at least one positive electrode tab having a firstattachment end and a second attachment end, wherein the first attachmentend of said at least one positive electrode tab is connected to saidpositive electrode current collector; at least one negative electrodetab having a first attachment end and a second attachment end, whereinsaid first attachment end of said at least one negative electrode tab isconnected to said negative electrode current collector; wherein thepositive electrode current collector comprises a conductive non-metalsubstrate.
 2. The cell of claim 1, wherein the positive electrodecurrent collector is a conductive carbon sheet selected from the groupconsisting of a graphite sheet, a carbon fiber sheet, a carbon foam, acarbon nanotube film and a mixture thereof, each of which has anin-plane electronic conductivity of at least 1000 S/cm; and wherein eachof the tabs is made of an electrically conductive material.
 3. The cellof claim 1, wherein the in-plane electronic conductivity of theconductive carbon sheet is at least 2000 S/cm.
 4. The cell of claim 1,wherein the in-plane electronic conductivity of the conductive carbonsheet is at least 3000 S/cm.
 5. The cell of claim 1, wherein thepositive electrode and the positive electrode tab form an interface,wherein the resistance of the interface is less than about 25 mOhm-cm².6. The cell of claim 1, wherein the resistance of the interface is lessthan about 2.5 mOhm-cm².
 7. The cell of claim 1, wherein said at leastone positive electrode tab is a plurality of metal tabs attached to thepositive electrode current collector.
 8. The cell of claim 2, whereinthe positive electrode current collector, the negative electrode currentcollector or both comprise a graphite sheet.
 9. The cell of claim 2,wherein the positive electrode current collector, the negative electrodecurrent collector or both are treated with a resin.
 10. The cell ofclaim 2, wherein the electrically conductive material is a metalselected from the group consisting of copper, nickel, chromium,aluminum, copper, titanium, stainless steel, gold, tantalum, niobium,hafnium, zirconium, vanadium, indium, cobalt, tungsten, tin, beryllium,and molybdenum and alloys thereof.
 11. The cell of claim 1, wherein thepositive electrode materials are transition metal oxides, phosphates andsulfates, or a lithium insertion transition metal oxide having a formulaselected from the group consisting of Li_(x)MO₂, M′_(2-y)O₄, LiV₂O₅,LiV₆O₁₃, Li_(x″)M″XO₄ and Y_(x′″)M′″₂(XO₄)₃, wherein: M is a transitionmetal selected from the group consisting of Mn, Fe, Co, Ni, Ti, V and acombination thereof and the subscript x is a real number between about0.01 and about 1; M′ is a transition metal selected from the groupconsisting of Mn, Co, Ni, Ti, V and a combination thereof, the subscriptx′ is between about −0.11 and 0.33 and the subscript y is a real numberbetween about 0 and 0.33; M″ is a transition metal selected from thegroup consisting of Fe, Mn, Co, Ni, and a combination thereof, X isselected from the group consisting of P, V, S, Si and a combinationthereof and the subscript x″ is a real number between about 0 and 2; Yis Li, Na or a combination thereof, M′″ is a transition metal selectedfrom the group consisting of Fe, V, Nb, Ti, Co, Ni and a combinationthereof, X is selected from the group consisting of P, S, Si, and acombination thereof and the subscript x′″ is a real number between 0 and3; and wherein the positive electrode materials are optionally dopedwith a metallic cation selected from Fe²⁺, Ti²⁺, Zn²⁺, Ni²⁺, Co²⁺, Cu²⁺,Mg²⁺, Cr³⁺, Fe³⁺, Al³⁺, Ni³⁺, Co³⁺ or Mn³⁺.
 12. The cell of claim 1,wherein the positive electrode material is a positive electrode activematerial comprising phosphates, sulfates, a lithium insertion transitionmetal oxide selected from the group consisting of LiCoO₂, spinelLiMn₂O₄, chromium-doped spinel lithium manganese oxide,xLi₂MnO₃(1−x)LiMO₂, LiNi_(y)Mn_(1-y)O₂, LiMO₂, LiNi_(x)Co_(1−x)O₂ andvanadium oxide or LiMPO₄ or LiFeTi(SO₄)₃; wherein: M is selected fromNi, Co or Mn; M′ is selected from the group consisting of Fe, Ni, Mn andV; and x and y are each independently a real number between 0 and
 1. 13.The cell claim 2, wherein the carbon sheet has a thickness of about 10μm to about 1000 μm.
 14. The cell of claim 2, wherein the carbon sheetoptionally comprises less than 5% of a conductive additive selected fromthe group consisting of carbon black, carbon fiber and carbon nanotubes.15. The cell of claim 2, wherein the carbon sheet has a purity of atleast 95%.
 16. The cell of claim 1, wherein the negative electrodematerial is a negative electrode active material selected from the groupconsisting of graphite microbeads, natural graphites, carbon fibers,graphite flakes, carbon nanotubes, Li metal, Si, Sn, Sb and Al.
 17. Thecell of claims 16, wherein the negative electrode current collector isselected from the group consisting of a metal foil and a carbon sheetselected from a graphite sheet, a carbon fiber sheet, a carbon foam, acarbon nanotube film or a mixture thereof.
 18. The cell of claim 17,wherein the metal foil is copper foil.
 19. The cell of claim 17, whereinthe metal foil has a thickness between about 5 μm and 300 μm.
 20. Thecell of claim 17, wherein the negative electrode current collector is acarbon sheet having the thickness between about 10 and 1000 μm.
 21. Thecell of claim 1, wherein each of the second attachment ends isoptionally coupled to an electrically conductive member for connectingto an external circuit.
 22. The cell of claim 1, wherein the ionconductive layer is an ion conductive membrane or a microporous layer.23. The cell of claim 1, wherein the electrolyte solution comprises asalt selected from the group consisting of LiPF₆, LiBF₄, LiClO₄ and acompound having the formula:(R^(a)SO₂)N⁻Li⁺(SO₂R^(a)), wherein each R^(a) is independentlyC₁₋₈perfluoroalkyl or perfluoroaryl.
 24. The cell of claim 23, whereinthe electrolyte solution comprises a salt selected fromCF₃SO₂N⁻(Li⁺)SO₂CF₃, CF₃CF₂SO₂N⁻(Li⁺)SO₂CF₃, CF₃CF₂SO₂N⁻(Li⁺)SO₂CF₂CF₃,CF₃SO₂N⁻(Li⁺)SO₂CF₂OCF₃, CF₃OCF₂SO₂N⁻(Li⁺)SO₂CF₂OCF₃,C₆F₅SO₂N⁻(Li⁺)SO₂CF₃, C₆F₅SO₂N⁻(Li⁺)SO₂C₆F₅ or CF₃SO₂N⁻(Li⁺)SO₂PhCF₃.25. The cell of claim 24, wherein the electrolyte solution comprisesCF₃SO₂N⁻(Li⁺)SO₂CF₃.
 26. The cell of claim 1, wherein the electrolytesolution comprises a solvent selected from the group consisting of alactone, ethylene carbonate, propylene carbonate, dimethylcarbonate,diethylmethylcarbonate and mixtures thereof.
 27. The cell of claim 1,wherein at least one first attachment end of the tabs has a smoothsurface.
 28. The cell of claim 1, wherein at least one first attachmentend of the positive electrode tabs, the negative electrode tabs or bothelectrode tabs comprises an array of preformed micro indentations,wherein each indentation is about 1-100 μm in depth and about 1-500 μmin dimension.
 29. The cell of claim 28, wherein said array ofindentations is evenly spaced.
 30. The cell of claim 28, wherein thefirst attachment end of each tab has a shape independently selected fromthe group consisting of a circle, an oval, a triangle, a square, adiamond, a rectangle, a trapezoidal, a U-shape, a V-shape, an L-shapeand an irregular shape.
 31. The cell of claim 28, wherein the firstattachment end of each tab has a dimension of at least 500 μm in widthand 5 mm in length.
 32. The cell of claim 1, wherein at least one firstattachment end of the positive electrode tabs, the negative electrodetabs or both electrode tabs is in direct contact with the positiveelectrode current collector.
 33. The cell of claim 1, wherein at leastone first attachment end of the positive electrode tabs, the negativeelectrode tabs or both electrode tabs is in contact with the positiveelectrode current collector through a conductive layer.
 34. The cell ofclaim 33, wherein the conductive layer is in contact with the surface ofsaid at least one positive electrode tab, negative electrode tab or bothelectrode tabs.
 35. The cell of claim 33, wherein the conductive layerhas a thickness of about 1 nm to about 100 μm.
 36. The cell of claim 33,wherein the conductive layer comprises a conductive filler and a binder.37. The cell of claim 36, wherein the conductive filler is selected fromthe group consisting of carbon black, conducting polymers, carbonnanotubes and carbon composite materials.
 38. The cell of claim 36,wherein the binder is selected from the group consisting of a polymer, acopolymer and a combination thereof.
 39. The cell of claim 1, whereineach of the first attachment ends comprises an array of preformed microopenings having a plurality of protruding edges, wherein each said arrayof preformed micro openings has a dimension of about 1-1000 μm.
 40. Thecell of claim 39, wherein said array of openings is evenly spaced. 41.The cell of claim 39, wherein said array of openings has a shapeselected from the group consisting of a circle, an oval, a triangle, asquare, a diamond, a rectangle, a trapezoidal, a rhombus, a polygon andan irregular shape.
 42. The cell of claim 1, wherein the positiveelectrode tab, the negative electrode tabs or both electrode tabs are incontact with a protective coating selected from the group consisting ofanodizing and oxide coatings, conductive carbon, epoxy and glues andpaints or a layer of metal selected from copper, nickel, chromium,aluminum, titanium, stainless steel, gold, tantalum, niobium, hafnium,zirconium, vanadium, indium, cobalt, tungsten, tin, beryllium,molybdenum or chromium.
 43. The cell of claim 1, wherein the positiveelectrode tab, the negative electrode tabs or both electrode tabs are incontact with a layer of metal selected from nickel, silver, gold,palladium, platinum or rhodium.
 44. A method of connecting a tab to anelectrode in an electrochemical cell, said method comprising: (a)providing an electrode comprising an electrode active material and acarbon current collector, wherein the electrode active material is inelectronically conductive contact with the carbon current collector; (b)providing a tab having a first attachment end for connecting to theelectrode; and (c) connecting the first attachment end of the tab to thecarbon current collector through a process selected from the groupconsisting of riveting, staking, conductive adhesive lamination, hotpress, ultrasonic press, mechanical press, crimping, pinching and acombination thereof.
 45. The method of claim 44, further comprising:depositing to said tab a protective coating selected from the groupconsisting of anodizing and oxide coatings, conductive carbon, epoxy andglues and paints or a layer of metal selected from copper, nickel,chromium, aluminum, titanium, stainless steel, gold, tantalum, niobium,hafnium, zirconium, vanadium, indium, cobalt, tungsten, tin, beryllium,molybdenum or chromium.
 46. The method of claim 44, further comprising:depositing a layer of metal selected from nickel, silver, gold,palladium, platinum or rhodium for improving the conductivity of thetab.
 47. The method of claim 44, wherein step (c) comprises aligning thecarbon current collector with the tab; and applying riveting, staking,conductive adhesive lamination, hot press, ultrasonic press, mechanicalpress, crimping, pinching or a combination thereof to the carbon currentcollector.
 48. The method of claim 47, wherein the tab has a shapeselected from the group consisting of a circle, an oval, a triangle, asquare, a diamond, a rectangle, a trapezoidal, a U-shape, a V-shape, anL-shape and an irregular shape.
 49. The method of claim 48, wherein thecarbon current collector is aligned to a predetermined point of the tab.50. The method of claim 44, wherein the tab is directly connected to thecurrent collector through staking.
 51. The method of claim 44, whereinstep (b) comprises piercing said attachment end of the tab to generatean array of openings having a plurality of protruding edges along theopenings for connecting to the current collectors.
 52. The method ofclaim 44, wherein the tab is connected to the carbon current collectorthrough a conductive adhesive layer.
 53. The method of claim 52, whereinthe conductive adhesive layer has a thickness of about 1 nm to about 100μm.
 54. The method of claim 52, wherein the conductive layer comprises aconductive filler and a binder.
 55. The method of claim 54, wherein theconductive filler is selected from the group consisting of carbon black,conducting polymers, carbon nanotubes and carbon composite materials.56. The method of claim 52, wherein the binder is selected from thegroup consisting of a polymer, a copolymer and a combination thereof.57. The method of claim 52, wherein the conductive layer is a conductiveadhesive layer.
 58. The method of claim 44, wherein the attachment endof the tab has an array of preformed micro indentations, wherein eachindentation is about 1-100 μm in depth and about 1-500 μm in dimension.59. The method of claim 44, wherein the array of indentations is evenlyspaced.
 60. The method of claim 44, wherein the tab is made from a metalselected from the group consisting of copper, nickel, aluminum andaustenitic nickel-based superalloys (INCONEL™), tantalum, niobium,hafnium, zirconium, vanadium, indium, cobalt, tungsten, beryllium andmolybdenum.
 61. The method of claim 44, wherein the tab is made from ametal selected from the group consisting of copper, nickel, chromium,gold, tantalum, niobium, hafnium, zirconium, vanadium, indium, cobalt,tungsten, beryllium and molybdenum and alloys thereof.
 62. The method ofclaim 44, wherein the attachment end has a dimension of at least 0.25mm².
 63. The method of claim 44, wherein the carbon sheet is selectedfrom the group consisting of a graphite sheet, a carbon fiber sheet anda carbon nanotube sheet or a blend thereof.
 64. The method of claim 63,wherein the carbon sheet is graphite sheet.
 65. The method of claim 63,wherein the carbon sheet has a thickness from about 10 μm to about 300μm.
 66. The method of claim 44, wherein the electrode is a positiveelectrode or a negative electrode.
 67. A battery comprising: a housing;a positive connector; a negative connector; a electrochemical cell ofclaim 1 disposed in said housing; and wherein said positive connectorand said negative connector are mounted on said housing.
 68. The batteryof claim 67, wherein: the positive connector has an inner end disposedwithin said housing and an outer end protrudes outside said housing; thenegative connector has an inner end disposed within said housing and anouter end protrudes outside said housing; and wherein said at least onepositive electrode tab is welded to the inner end of the positiveconnector and said at least one negative electrode tab is welded to theinner end of the negative connector.
 69. The battery of claim 67,wherein the positive connector is said at least one positive electrodetab and the negative connector is said at least one negative electrodetab, wherein the second attachment end of said at least one positiveelectrode tab and the second attachment end of said at least onenegative electrode tab protrude outside said housing.